Control device



Dec. 6, 1949 A. R. DAVIDSON CONTROL DEVICE Filed March 31, 1945 RELAY TRA/XS/ I INVENTOR.

ATTORNEY.

Patented Dec. 6, 1949 UNITED STATES PATENT OFFICE CONTROL DEVICE Allen B. Davidson, Erie, Pa., assignor to Reliable Radio Inc., Erie, Pa., a corporation of Pennsyl- Vania Application March 31, 1945, Serial No. 585,878

7 Claims. 1

This invention relates to a control device actuated by the change in transmission of radio frequency energy between a pair of electrodes due to the presence of a foreign body in the field between the electrodes. One application is as a safety device for a machine where the operator must reach through the field between the electrodes to get to a danger zone. The interception of the field by the operator changes the signal received at one of the electrodes causing operation of the control to prevent injury to the operator. Further objects and advantages appear in the specification and claims.

In the accompanyin drawing, Fig. 1 is an elementary diagram; Fig. 2 is a fragmentary view showing the electrodes arranged as a safety device for a molding press; and Fig. 3 is a control diagram.

The control device is actuated by changes in the field between transmitting and receiving electrodes 1 and 2 connected across a radio frequency transmitter 3. The transmitter is diagrammatically illustrated as having a center tapped output inductance 4, one end connected directly to the transmitting electrode and the other end connected through a coupling condenser 5 to the receivin electrode. The coupling condenser conducts an out of phase voltage to the receiving electrode substantially balancing the voltage received from the transmitting electrode. Since the electrodes are closely spaced, only the induction field radiation is transmitted to the receiving electrode. When the field between the electrodes is disturbed, the net radio frequency energy at the receiving electrode is changed, and this change is fed through an amplifier 6, a detector 1, to a relay 8 for performing the desired control function.

The shape and position of the electrodes will obviously vary with the control application. In Fig. 2 the control is shown applied to a molding press having a stationary platen 9 and a movable platen In. The electrodes are arranged in front of the press to interpose a curtain-like field between the press and the operator. The transmitting electrode is in the form of a plate arranged edgewise to the press and spaced sufficiently in front of the press so that the field between the electrodes is negligibly affected by the movable platen. The receiving electrode is in the form of a rod similarly spaced in front of the stationary platen. The electrodes have a height slightly greater than the height of the platens so that an operator reaching between the platens must intercept the field beween the 2 electrodes. In a practical application the electrodes have been spaced about three inches from the press and the spacing between the electrodes has been eighteen inches.

An operator reaching between the electrodes causes an increase in the radio frequency energy at the receiving electrode. This increase in energy is used to actuate the relay which may be a solenoid ll having normally closed contacts I2 connected in the control circuit for closin the press, and contacts 13 connected in the control circuit to open the press. The increase in radio frequency energy at the receiving electrode causes the closure of the contacts l3 and the resultant opening of the molding press.

After the press is closed, the control is no longer necessary. The control is therefore disabled by a limit switch l4 mechanically connected with the movable platen so as to open contacts I5 when the press is closed. The opening of the contacts I5 prevents opening of the molding press by the closing of the contacts l3.

In the control diagram, the transmitter is shown as a three megacycle oscillator supplied by a full wave rectifier l 6. The output circuit of justed so that the bridge is normally nearly balanced. Sensitivity is greater if the bridge is slightly to one side of the balance point. Unbalancing of the bridge caused by the operator reaching between the electrodes results in an increase in voltage at the receiving electrode which is coupled to the control grid IQ of the amplifier. The amplifier output appears in a tuned circuit 20 inductively coupled to a tuned circuit 2| in series with the detector I. The detector output.

is taken from the cathode circuit from a condenser 22 shunted by a resistance 23. An increase in the radio frequency voltage at the receiving electrode 2 appears in the detector output as a positive voltage which is connected to the control grid 24 of a thyratron 25. The thyratron is connected in series with the solenoid release H across the secondary 26 of a transformer 21. The cathode 28 of the thyratron is connected to an adjustable tap 29 on a voltage divider 30 across the full wave rectifier l6. An additional not affect the thyratron. When the operator reaches between the electrodes, the further increase in radio frequency energy at the receiving electrode causes a positive bias on-thegrid: 24

which overcomes the bias from the tap 2-9-and fires the thyratron. This actuates the solenoid relay Ii opening the contacts lzcand clpsine h contacts I3. The opening of the contacts l2 prevents further closure of the press and the closing of the contacts !3 opens'the press.

The control can .be made very sensitive with.- out becoming sosensitive as toresult in nuisance operation. Thecontrol is made insensitive, ex-

cept in the field between the electrodes. The con-v trol will be actuated as soon as the operators finger reaches the-field between the electrodes. It will not be actuated by movementof the platen nor will it be operated if the operators hand is placed quite close to the-outside of eitherof the electrodes. For example, the operators hand can be placed withina few inches of the trans-. mitting electrode on-the outer side-without :making any substantial change in theradio frequencyenergy received atthereceiving electrode. This indicates that the control' is almost whollyre-. sponsive to the field betweenthe electrodes. By increasing the positi-v ebi'asat the adjustable tap 29, the control maybe made less sensitive. As the sensitivity isdecreased the area of response between the electrodes is-decreased until'finally the control will-be-actuated only lithe-operatorrcaches through'thecenter pointof-thefield between the electrodes. Undertheseconditions the operator can take hold of either electrode without operating thecontrol. r 7

As the electrodes are spacedfurtherapart, the operation is improved byconnecting a condenser 3 3 across theelectrodes. Thecondenser 34"couples an in phase voltage to the-receiving'electrode partially balancing the-outof phase voltage from thecondenser Inthe-specific application the condenser 35 wasfound desirable when the electrode spacing-was increased 'frorn twelveto eight-- een inches. In the particular application the condenser 3-:- permits the'selection om practicalvalue for the condenser It-isnot necessary in all applications. 7

The intensity or the fieldbetween the electrodes is greatest in the area b unded-"by'lines of sightconnecting the outside edges of the electrodes. There is a field of lessintensity-outside'this area. By adjustingthe sensitivity control it-is possible tomalze the device respond'to interception of the field in the area bounded by the electrodes; to interception of only thefield at the central part ofthe area, or to interception of the-lower intensity field outside thearea, The adjustment depends upon the requirements of the application.

The shape of the electrodes also-varies with the application. In the applicationillustrated, thereceiving electrodeis arod because itis-located near'the normal position of the operator. The smaller area of the rod-presented to the operator minimizes accidental operation of the-safety device. If both electrodes wererods (orwires) 4 the sensitivity control would have to be adjusted for greater sensitivity and the part of the field responding to interception by the operator would be thicker (would bulge) at the center. This is not desirable for the application illustrated, where a zone of response of limited thickness is required to prevent nuisance operation of the safety device. For other applications a thicker zone of response may not be objectionable and may even be desirable.

By having the control respond to interception of the field between two electrodes rather than to interception of the field between one of the electrodes and ground, the operation is substantiallyindependentof the intercepting body which may be grounded or insulated or isolated from ground without; affecting the operation of the control.

What I claim as new is:

1. In a control circuit, a bridge having a pair of inductiveand a pair. of ,capacitative arms, a

radio frequency supply connectedacross the? brid e, one of the arms comprising a pair of spaced electrodcsghaving asubstantial impedance to groundandaradio frequency field onilines of sight therebetween in which the. presence of a. foreign body is to bedetected, anda. control responsive to thechangein Volta e-across the electrodes due to, the presence of; a foreign body in the field.

2. In a control circuit, a, radio frequency source having a center tapped, output coil, a capacity divider across the coil", said capacity dirid r havin a en er terminal and on one side of, the terminal a pair of electrodes havinga sub-- stantial imp lance to ground anda field onlines of sight therebetweenin which the presence of a. conducting or semiconducting foreign body is to, be; detectedand on, the other side of'the terminal a balancing condenser, an amplifier for the volting=,,adjusted-so the control is operated by. the

change in interelectrode capacity due to the;

. presence of, aiorcign body in said field.

v 3.;In ;a c ontrol circuit, transmitting. and ;--receiving electrodesspaced; to provide a field inlines:

of sight the-rebetween;affectedgby thepresenceof a;;foreign body...a,:ra dio frequency transmitter;

electrode of. phaseoppositeto the wave from'the.

transmitter; electrode substantially balancing the transmitted wave, acondensercoupling a radio frequency wave tothe receiving electrode inphase. with the transmitted wave; and means responsiveto the change in-thenet radio frequency wave, at the receiving electrodeldueto the change in the-transmitted wave caused-bye lbody intercepting'the field.

4-. .In, a, control. circuit, spaced electrodes having, a substantial impedance to ground and energizedby aradio frequencypower sourceproducing a radio frequency field: on: lines of :sight; therebetween in which the presence of a conducting 'orsemieoonducting :foreign body is to be. detected. a: bridgecircuit, having an arm in cluding the electrodes,andacontrol responsive to changein the balance ofthe bridge caused by the presenceota ioreignJbQ'dy inthefield:

:5. A safety device for a machine haVing-amoV- in part, a pair of electrodeslhaving a substan tial impedance to ground and tosaid part and energized by: a radio: frequency power sourcepro ducing -a curtain like-radio frequency field on lines of sight between said electrodes and shielding said part from the operator, the electrodes being to one side of said part so the field is negligibly affected by the position of the part, a bridge having diametral terminals for connection to a radio frequency source and having an arm including the electrodes, and a control for the safety device responsive to the change in voltage at an intermediate terminal on the bridge due to the interception of said field by an operator.

6. In a control circuit, transmitting and receiving electrodes having a substantial impedance to ground and spaced to provide a radio frequency field on lines of sight therebetween affected by the presence of a, foreign body, a radio frequency transmitter connected to the transmitting electrode and energizing the electrode at a substantially constant intensity and frequency, means coupling a radio frequency wave to the receiving M electrode of phase opposite to the wave from the transmitter electrode, and means responsive to the change in the net radio frequency wave at the receiving electrode due to the change in the transmitted wave caused by a body intercepting the field.

'7. A safety device for a machine having a danger zone, transmitting and receiving electrodes having a substantial impedance to the machine and to ground and spaced to provide a radio frequency field on lines of sight between the ALLEN R. DAVIDSON.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,958,128 Cate May 8, 1934 1,962,742 Jongedyk June 12, 1934 1,971,549 Woodward Aug. 28, 1934 2,041,114 Carini May 19, 1936 2,053,668 Davis Oct. 27, 1936 2,115,322 Wood Apr. 26, 1938 2,152,296 Weis et al. Mar. 28, 1939 2,313,912 Brownlee Mar. 16, 1943 2,333,001 G-oldstine Oct. 26, 1943 2,355,395 Rubenstein Aug. 8, 1944 2,386,942 Edelman Oct. 16, 1945 2,395,780 Devol, Jr., et al. Feb. 26, 1946 

